Water is involved in a cycle called the
“hydrologic cycle”, so it is not possible to put a
figure on the age of water. However, water has
been on the planet for at least 4.4 billion years
in the oceans.

Answer 2:

It looks like in early 2013, scientists
discovered a pocket of underground water that is
around 2.6 billion years old!

Answer 3:

It depends on what we mean by "old". Fluid
inclusions in rocks are known from I believe
upwards of three billion years, maybe longer. All
of the water in our solar system was here already
when the solar system formed, though, which was
4.7 billion years ago. Water itself is made of
hydrogen and oxygen. Hydrogen was made in the big
bang, and oxygen was cooked in giant stars that
went supernova. When the supernovae happened that
spiked the solar system with oxygen we will
probably never know.

Answer 4:

The amazing thing about water is that virtually
all the water that is here has been here since the
Earth formed. Although scientists can create and
destroy small amounts of water in experiments, all
the other water has been unchanged. The water is
continually recycled through the water cycle of
evaporation and precipitation (for example, rain
and snow), but the water you drink is billions of
years old.